The Church of St. John the Baptist is a domed cruciform church, built of undressed stone. It is one of the best preserved churches in Nesebar. It is 12 meters long and 10 meters wide. The structure of the church consists of two cylindrical vaults which intersect in the center of the composition. The masonry is crushed stone and pebbles and the facades were probably smoothly plastered. It was built in the 11th century. The altar space consists of three semi-circular apses. Four massive pillars support the dome and form the cross. Inside the church the walls are smooth and unbroken. The exterior is simple without decorative niches and ceramic plaques, typical of the ornamental style. Bricks were used as a decorative element over the entrance, in the jagged cornices and around the windows.
Some frescoes in the church have been preserved dating from later periods. The faded portraits of the donor and his contemporaries on the southern wall and the fragments beneath the dome date from the 14th century and the others are from the 16th and 17th centuries.
The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.